After traveling hundreds of thousands of miles through space over the last month, NASA’s revolutionary new James Webb Space Telescope performed its last big course correction maneuver this afternoon, putting itself into its final resting place in space. Now, the observatory will live in perpetuity at a distance of roughly 1 million miles from the Earth, giving the vehicle a front-row view of the most ancient stars and galaxies of the Universe.

Launched on Christmas Day, NASA’s James Webb Space Telescope, or JWST, has had a wild ride to its destination. Too enormous to fly to space in its final form, the telescope had to launch folded up inside its rocket. Once it reached space, JWST began an extremely complex routine of shape-shifting and unfurling, a type of choreography that no spacecraft had ever performed before. Yet JWST performed every step flawlessly, completing its major deployments on January 8th and blossoming into its full configuration.

Plenty of anxiety surrounded those deployments, as they had to work as planned; one failure could have jeopardized JWST’s entire mission. But the mission team’s unease didn’t end when unfurling was complete. JWST still had to get into its final position in space in order to do its job properly. If the observatory didn’t slow down just right today, the vehicle ran the risk of getting into the wrong orbit or missing its target trajectory completely. Such a failure could have complicated the mission’s future, making it incredibly difficult for scientists to communicate with the nearly $10 billion space observatory.

Fortunately, JWST performed this last maneuver flawlessly. “During the past month, JWST has achieved amazing success and is a tribute to all the folks who spent many years and even decades to ensure mission success,” Bill Ochs, the JWST project manager at NASA’s Goddard Space Flight Center, said in a statement.

Though it’s been a month getting to this point, it didn’t take long for JWST to put itself into its final destination this afternoon. At around 2PM ET, JWST fired its onboard thrusters for roughly 5 minutes. It was the last of three course correction burns that JWST has done, slowing the spacecraft down enough to put it into a very precise orbit in space.

JWST is now orbiting around an invisible point in space known as an Earth-Sun Lagrange point. It’s a somewhat mystical area of space where the gravity and centripetal forces of the Sun and the Earth are just right, allowing objects to remain in a relatively “stable” position. “There’s a little tug of war going on where [gravity] balances out perfectly,” Jean-Paul Pinaud, the ground operations delta-V lead at Northrop Grumman, the primary contractor of JWST, tells The Verge. “So nobody wins that tug of war.”

The Sun and the Earth share five of these Lagrange points, peppered around our planet. There’s one directly in between the Earth and the Sun and one on the opposite side of our star from us. JWST is orbiting around one Lagrangian point located on the far side of the Earth further from the Sun, called L2. In this position, as Earth moves around the star, JWST will follow the planet almost in lockstep, like a constant companion always in the same location in relation to our planet. No matter where Earth is on its course around the Sun, JWST is guaranteed to be about 1 million miles away from us.

The track that JWST is taking around L2 is actually fairly wide, stretching roughly the distance between the Earth and the Moon. But the observatory can’t stay on that trajectory forever without some help. L2 is what’s known as “pseudo” stable, meaning objects that orbit this location will have a tendency to drift away in one direction. “It’s like sitting on a saddle of a horse,” Pinaud says. “On a saddle of a horse, you’re kind of stable. Imagine yourself as being a marble… from head to tail, you’ll probably roll down to the center, but then once you go to either side of the saddle, you’re just gonna fall to the ground.”

So JWST will have to make small adjustments to its path over its lifetime. Every 20 days or so, the telescope will fire its thrusters for two to three minutes at a time to ensure that it stays on track in its orbit. Ultimately, these adjustments will determine how long JWST can stay active in space. When the propellant runs out in the next 10 to 20 years, that’s when the observatory’s mission will end. (Luckily, JWST’s ride to space, the Ariane 5 rocket, put it on such a great trajectory that the telescope’s lifespan will last way longer than originally predicted.)

It may seem like a complicated position, with a lot of extra effort needed to keep JWST stable. But L2 is a pretty attractive place for this observatory for a variety of reasons. Perhaps the biggest advantage is how far away it is from both the Earth and the Sun. JWST was made to collect infrared light, a type of light that is associated with heat. Because of this design choice, the telescope must remain extremely cold at all times. That’s why it’s equipped with a sunshield that will always be facing the Sun, a protective umbrella that will reflect the star’s heat and keep the telescope extra frigid. Still, any nearby object emitting heat and infrared light could muck up JWST’s observations if NASA isn’t careful. By putting the telescope nearly 1 million miles away from our planet, NASA is guaranteeing that the infrared light coming from the Earth and the Moon will not interfere or heat up the telescope.

L2 is also great from a power standpoint because one side of JWST will always be facing the Sun. On that heated side, the telescope has a solar panel that is constantly gathering sunlight for power. Other spacecraft, such as the Hubble Space Telescope in orbit around Earth, don’t have that luxury. Whenever Hubble orbits on the nightside of Earth, it loses the view of the Sun and must store power in its batteries. That will never be the case for JWST. “We have basically limitless power for mission operations, and we don’t have to worry about any eclipses,” Kyle Hott, the mission systems engineering lead for JWST at Northrop Grumman, tells The Verge.

There are also some downsides of constantly switching between day and night when orbiting the Earth; the extreme fluctuations in temperature can jostle and vibrate a spacecraft, causing its instruments to degrade over time. JWST will operate at roughly the same temperatures all throughout its lifetime.

And then there is the benefit of continuous communication. With L2 always in the same position relative to Earth, JWST will be a set distance away from our planet at all times. That means we can be in constant contact with the observatory. “We can sort of be tugged along at L2 by the Earth-Sun system, such that we have that nice convenient constant communications with the vehicle,” says Hott. “And so that simplifies just a lot of the mission operations as well.”

This crucial finale caps off the observatory’s risky journey through the cosmos, paving the way for the science to finally begin. We still have to wait some more for JWST’s observations to get underway, though. Scientists and engineers will soon start aligning the telescope’s mirrors ever so precisely before commissioning the observatory, testing out all of its instruments to make sure they’re ready to collect the first extraordinary images of the most ancient stars and galaxies in the Universe.

That process will take many months, but if it goes well, the first historical images captured by JWST could be beamed back to Earth as soon as this summer.

https://www.theverge.com/2022/1/24/22895050/nasa-jwst-space-telescope-final-orbit-lagrange-point